An Italian scientist, Guglielmo Marconi, was one of the first scientist to send signal by radio in 1895. At first, radio message were sent in morse code. The first sound broadcast began in 1910.
Vibrating Signals
Radio waves are electric signals that vibrate from weak to strong, million of times a second, as they travel. All radio waves travel at a speed of 299,792 kilometres per second that' the speed of light.
Imagine that you could see radio waves as they passed you. You would find that they are all different. some radio waves vibrate more frequently. They have high amplitude. Some waves have a low frequency. The distance between one vibration and the next is longer than a high-frequency wave. This wave will have a longer wavelength.
Radio Broadcast
when radio waves are broadcast, they travell over different distances. Some waves, called long waves, travel parallel to Earth's surface, trapped between the Earth and a layer of the atmosphere calle the ionosphere. Another type of wave, calle short wave, bounces back off the ionosphere during the day time when ionosphere is dense. Other waves, called UHF (Ultra High Frequency), and VHF (Very High Frequency), can travel through the ionosphere and can be relayed by satellite.
Taken from : Young Scientist : Communicating, 1996
pic: credit 2 Google.com
